The objective of this project is to study specificities of macrocyclic ligands for cations as a function of (a) cation charge, size, and type; (b) ligand cavity size; (c) ring substituent and of type, number, and spatial arrangement of both ligand and donor atoms; (d) the counter anion; and (e) the solvent. The following studies will be carried out during the year: (1) Continue the calorimetric investigation of the interaction of selected metal ions with substituted crown ethers, e.g., polyether-ester and pyridyl substituted ethers, to find various selectivity sequences for metal ions; (2) Continue to look for structural features that may play a role in changing metal selectivity sequences.